Hitherto, there is known a stator for a motor, which is constituted with a ring-shaped yoke portion iron core, tooth portion iron cores arranged at an equal interval on the inner circumferential side of the yoke portion iron core, and stator coils fitted into slots formed between respective adjacent tooth portion iron cores, wherein a rotor is oppositely disposed through a gap on the inner circumferential side of the tooth portion iron cores. In this case, there is disclosed a stator core in which the inner circumferential sides of respective adjacent tooth portion iron cores are connected by portions serving as a bridge between magnetic poles (hereinafter simply referred to as bridging portions) having a small cross section in order not to take the stator assembly to pieces at the time of punching or assembling of tooth portion iron cores and yoke portion iron core, and to reduce leakage reactance (e.g., the Japanese Patent Application Laid Open No. 196034/1987 (Tokkaisho No., 82-196034), the,Japanese Patent Application Laid Open No. 174531/1988 (Tokkaisho No. 63-174531).
However, with the above-described configuration, there were the drawbacks that the cogging torque cannot be sufficiently small and/or unevenness of the cogging torque becomes greater in dependency upon the dimensions of tooth portion iron cores employed.